Insects sometimes cause massive damage to landscape plants, but these instances are usually rare occurrences. It's only when the insect populations reach a certain critical mass that the damage becomes troublesome.
Most insects pose no problems at all to lawn and landscape plantings. Often, many insects are predators of other insects that are harmful. Therefore, we need to be very careful about using insecticides that will kill all the insects in a given area.
For the most part, you can ignore most insects in the landscape. There are some exceptions: particular attention should be given to Japanese beetles (steps should be taken as soon as they appear in the landscape).
Plants damaged by the majority of insects include leaf problems. Identifying the type of leaf problems you have will help in identifying the particular insect that is causing the damage. The following are a grouping of types of insects associated with particular leaf problems. This list is by no means exhaustive, but tries to give the reader an insight into some of the more common insect problems.
Eaten leaves are where you can see a portion of the leaf is missing. Insects that typically eat leaves are the following:
|Asparagus beetles||asparagus||leaves are eaten, the epidermis is removed from stems causing the upper growth to dry and turn brown.|
|Black vine weevils||yews, rhododendrons, hydrangeas, euonymus, camellias, grapes, strawberries and fuchsias||notches appear in leaf margins, often near the ground from late spring to mid fall.|
|Caterpillars||many garden plants||leaves and occasionally flowers are eaten away from the edges inward|
|Colorado potato beetles||potatoes, tomatoes, eggplants, peppers||leaves are eaten, leaving only the main vein.|
|Earwigs||shrubs, perennials, annuals including dahlias, chrysanthemums, clematis, apricots and peaches||young leaves and petals are eaten in summer|
|Flea beetles||seedlings, leafy vegetables, radishes, wallflowers||holes and pits appear on upper surface of leaves; plants may die if attack is severe|
|Gypsy moths||many deciduous trees and shrubs, but especially apples, hawthorns, oaks, lindens and sometimes conifers such as spruce||leaves are eaten and plants may be defoliated. Repeated attacks will kill the plant.|
|Japanese beetles||various plants including grape, roses, and daylilies||flowers and leaves are eaten often in groups, leaving only the veins of the leaf visible.|
|Leaf-cutting bees||roses, some trees and shrubs||lozenge-shaped or circular pieces of uniform size are removed from the margins of the leave (outer edge)|
|Millipedes||seedlings and other soft growth plants including strawberry fruits and potato tubers||seedlings and soft growth are eaten, roots and stems may be eaten during dry periods; damage is rarely serious|
|Plant bugs||shrubs and perennials, especially chrysanthemums, asters, gladioli, zinnias, mint and dahlias, some annuals and fruits||leaves at shoot tips are distorted with small holes during the summer months|
|Sawfly larvae||trees, shrubs, perennials, bulbous plants and fruits; particularly affected are pines, willows roses, gooseberries and currants||plants are defoliated|
|Slugs and snails||all seedlings, climbing plants, perennials, hostas, small annuals, bulbous plants, vegetables including potatoes and strawberries||holes appear in the foliage and stems may be stripped; silvery slime trails may be left on the leaves; small holes are visible on the outside of bulbs and the underground part of their stems, leading to large cavities inside|
|Sowbugs and pillbugs||seedlings and other soft growth including strawberries||holes may appear in seedlings and in leaves near shoot tips, but sowbugs are not generally pests; they eat mainly decaying plant materials and are often found on plants that have already been damaged by other pests or diseases|
|Aphids||woody plants, perennials, annuals, bulbous plants, vegetables, fruits and indoor plants||leaves are often sticky with honeydew (aphid excrement) or blackened by sooty molds; stems and buds may also be covered|
|Lace bugs||rhododendrons, evergreen azaleas||pale green to yellow mottling on the upper leaf surface, with stick spots on the underneath side where feeding takes place|
|Leaf and bud nematodes||annuals, most herbaceous perennials, begonias, chrysanthemums||brownish black patches appear on leaves as islands or wedges between the larger leaf veins|
|Leafhoppers||trees, shrubs, perennials, annuals, vegetables and fruits; rhododendrons, roses, pelargonium's, primroses and tomatoes||coarse pale spotting appears on the upper leaf surface|
|Leaf miners||trees, shrubs, perennials, and vegetables, especially birch, hollies, apples, and chrysanthemums||white or brown areas appear within the leaf, often of characteristic shape for the particular leaf miner; these areas appear to be irregular paths inside the leaf structure|
|Leaftiers and leafrollers||trees both ornamental and fruit, shrubs, perennials, annuals and bulbous plants||2 leaves may be bound together with fine silk threads or one leave may be either similarly attached to a fruit or folded over on itself; brown, dry skeletal patches appear on the leaves|
|Mealybugs||succulents, vegetables, grapes, some tender fruits and citrus||a fluffy white substance appears in leaf and stem joints; plants may be sticky with honeydew and blackened with sooty molds; roots may also be affected|
|Psyllids (immature nymphs of small, aphid like, winged insects about 1/16" long)||bay, boxwood and pears||leave margins of bay are yellowed, thickened, curled; boxwood leaves are stunted; pear leaves are sticky with honeydew and blackened with sooty mold; damage occurs throughout the spring and summer|
|Scale insects||trees, shrubs, cacti and other succulents, fruits||foliage is stick with honeydew and blackened with sooty molds; plant growth may be slow; white, egg-containing deposits may also appear|
|Spider mites||trees, shrubs, perennials, annuals, bulbous plants, cacti and other succulents, vegetables and fruits; beans, melons, apples, and plums||leaves become dull and increasingly yellowed as a fine pale mottling develops on their upper surface; leaves fall prematurely and a fine silk webbing may cover the plant|
|Squash vine borers|
|Tent caterpillars||many deciduous trees||large white nests are spun in the forks of branches in spring; the larvae move out by day to feed on leaves, returning at night|
|Thrips||wide range of shrubs, perennials, annuals, bulbous plants, vegetables, fruits||silver-white discoloration with tiny black dots appear on the upper leaf surface|
|Whiteflies||affects both indoor and outdoor flowering plants and some vegetables, fruits||leaves are covered with stick honeydew and sooty mold; small white insects fly off when plants are disturbed|
Insects are not a common cause of residential lawn damage, but certain insect species occasionally damage or kill turfgrass.
Insect feeding can cause grass to turn yellow or brown, or die, especially if the grass is already stressed. Damage usually begins in scattered small patches, which may merge into large dead areas.
Lack of proper cultural care and use of inappropriate grass species in a particular location are more likely responsible for unhealthy or dying lawns than insects. Disease-causing pathogens, excessive or inappropriate use of chemicals such as fertilizers and herbicides, and dog urine also produce damage resembling that of insects. Before taking any insect control action, be sure that it is insects causing the problem and not something else.
Insects that do infest home lawns are often difficult to observe and their presence goes undetected until significant damage has been done. Plus, insect damage can be mistaken for other problems such as drought damage. If the lawn remains brown or shows signs of thinning despite appropriate watering, then closer examination for insects should be done. A lawn inspection should include looking at leaves, stems, roots, thatch and the soil to determine if the problem is insect-related and catch the problem before extensive damage occurs.
Insects that may cause damage lawns include various root-, crown-, and leaf-feeding caterpillars; white grubs, which are the larvae of beetles; billbugs, which are weevils with white, grub like larvae; and chinch bugs, which are true bugs in the order Hemiptera. Armyworms, cutworms, mole crickets also cause damage to lawns. In northwestern America, crane flies are sometimes a problem.
Each species produces somewhat different damage symptoms and must be managed differently. Many insects may be observed while examining grass. However, control is rarely or never needed for most types of insects because they are harmless, and more likely to be beneficial.
Common beneficial insects include predatory ants, ground beetles, rove beetles, and blister beetles. Other common arthropods that are primarily decomposers and do no significant injury to turfgrass include springtail's and millipedes.
Good cultural practices are the primary method for managing insect damage to lawns. Growing appropriate grass species for a particular location and providing lawns with proper care are especially important. Practices such as irrigating and fertilizing have a major impact on lawn health. Physical controls, such as thatch removal, choice of mowing height and frequency, and providing grass with more light by pruning tree branches, are also important in certain situations.
Most home lawns do not need to be treated with insecticides if proper cultural practices are followed. Insecticides should never be applied unless a pest is identified and detected at damaging levels. If insecticides are necessary, choose materials that have minimum impacts on beneficial organisms and the environment.
Keeping your grass healthy is by far the best way to prevent damage from lawn pests. Healthy lawns require few, if any, insecticide treatments. If a lawn is under stress and a pesticide is applied, it stands a better chance of suffering damage from the pesticide itself.